Thirty years after the big 1977 New York blackout, you’re even more likely to spend some of the summer sweltering without lights or air conditioning.

The number of blackouts of all kinds nationwide has increased since 1990 at a rate of 7.2 percent a year, and they’ve gotten longer, too, say researchers at New York University.

“The situation is not getting better,” said NYU Professor Rae Zimmerman, citing “evidence of a much greater stress on the system overall.”

In New York, some of that stress comes from greater electricity use.

Con Ed’s peak power load this week was about 70 percent higher than on the day of the 1977 black out. And though the company says it has spent billions, a lot of its cable and street equipment is 50 or 60 years old.

The inability of Con Ed’s equip ment to handle the electricity run ning through it was partly to blame for last summer’s nine-day blackout in Astoria and Long Island City, Queens, state investigators found.

Another problem is that New York’s grid is linked to the giant Eastern Interconnection, which stretches west to Colorado, south to the Gulf of Mexico and north to Manitoba.

It was a massive breakdown in Ohio’s power grid that plunged New York and most of the eastern United States into darkness in August 2003.

“The lower standards you have for operating the system, the more power you can move across it,” said power-industry consultant George Loehr.

The June 13-14, 1977, blackout – like the 2003 blackout – began outside the city, when lightning strikes north of the Big Apple knocked out major transmission lines.

A 1977 city report on the blackout concluded that among Con Ed’s many failings, it “did not provide its operators with adequate operating directives, training and display equipment.”

Today, more backup systems have been built into the state power grid, and its managers say they do a better job monitoring weather conditions.

But even if all of New York’s power grid is fully modernized, engineers say blackouts will still happen.

“Systems can fail,” said Loehr. “The equipment itself can fail, even if the plans and everything are virtually perfect.”